Increasing the divergence of a laser.

[will171]

I am slightly unsure about how the divergence can be increased by the use of either bi-concave or plano-concave lenses. I understand the general theory behind it but am having trouble putting numbers to it. e.g. if you have a laser beam with a diameter of 2mm and a divergence of 2mrad what focal length lens would be needed to increase its divergence to 5mrad/10mrad/etc? Any help would be greatly appreciated especially if it explains the calculations needed to work these things out.

 

[Andy Resnick]

A gaussian beam (most laser beams) have a really nice property- the product of divergence and beam waist is a constant. So, if the initial beam has a waist of 2 mm and divergence of 2 mrad and you want a divergence of 10 mrad, you only need focus the beam to a waist of 0.4 mm.

 

[astrokreng]

Increasing the divergence of a laser beam can be achieved by using bi-concave or plano-concave lenses. These lenses are designed to diverge light rays, causing the laser beam to spread out and increase its divergence.

To calculate the focal length of the lens needed to increase the divergence of a laser beam, we can use the following formula:

f = w/tan(θ)

Where:
f = focal length of the lens
w = diameter of the laser beam
θ = desired divergence angle in radians

For example, if we have a laser beam with a diameter of 2mm and a divergence of 2mrad, and we want to increase its divergence to 5mrad, we can use the formula to calculate the focal length of the lens needed:

f = 2mm/tan(5mrad) = 2mm/0.005 = 400mm

This means that we would need a lens with a focal length of 400mm to increase the divergence of the laser beam to 5mrad.

Similarly, if we want to increase the divergence to 10mrad, we would use the same formula but with a divergence angle of 10mrad:

f = 2mm/tan(10mrad) = 2mm/0.01 = 200mm

In this case, we would need a lens with a focal length of 200mm to increase the divergence of the laser beam to 10mrad.

I hope this explanation helps to clarify the calculations needed to determine the focal length of the lens needed to increase the divergence of a laser beam. It is important to note that these calculations are based on ideal conditions and may vary in practical applications. It is always best to consult with an expert or conduct experiments to determine the most suitable lens for your specific needs.